The present invention relates to a container with an easy open-type closure of such a type that the container is tightly closed at its opening end portion with a metallic foil sheet made closure. A strip shaped pull opening member, having at its one end a pulling tab, is fixed more firmly to the top surface of the closure than a tearing strength of the closure so that by lifting the pulling tab of the pull-opening member in relation to the closure, the closure may be torn open into a predetermined opening shape.
As for a container of this kind, there has been heretofore known a container such as that disclosed in Japanese Kokai Utility Model Application Publication Sho No. 54-97342, for instance, which shows a metallic foil sheet made closure tightly fixed to the opening end portion of the container barrel, with a pull-opening member firmly fixed to the closure. By pulling the pull-opening member, the closure may be opened by tearing.
This type of container, however, is defective in that although the closure is so arranged as to be torn open along the shape of the pull-opening member itself, it actually happens that the closure cannot be broken open definitely or neatly along a predetermined opening shape.
For making the container a more practicable one in which a closure can be torn open by a pull-opening member in a predetermined opening shape, it is necessary to satisfy the following three prerequisite points.
(1) It is necessary that, besides the pull-opening member, an opening edge for regulating an initial tear opening position is predetermined so that when the pull-opening member is pulled, the metallic foil sheet is applied with a reliable initial tearing, and then the tearing is advanced towards the predetermined opening edge, and thereafter the tearing is carried out definitely and neatly along its opening edge. PA1 (2) It is necessary that the pull-opening member is firmly adhered to the metallic foil sheet, and the adhesive strength thereof maintains a level above the tearing strength of the metallic foil sheet, even after a lapse of time. PA1 (3) It is necessary that the pull-opening member itself has a sufficient tensile strength to prevent it from being fractured when the metallic foil sheet is initially broken open and also that the tensile strength is maintained even after a lapse of time.
The inventors have made various investigations and research for obtaining a container wherein a metallic foil sheet made closure is fixed, together with a ring-shaped member, to an opening end portion of a container barrel, and a pull-opening member is fixed to the closure through an adhesive agent layer so that, by pulling upward on the pull-opening member, the closure may be torn open in a definite and neat manner to obtain a predetermined opening shape defined by the ring-shaped member.
As a result thereof, and with respect to prerequisite point (1) above, such a container has been developed and proposed by Japanese Kokai Utility Model Application Publication Sho No. 57-177932, wherein the closure of the container can be torn open in a definite and neat manner along a predetermined opening shape defined by the opening edge by forming the pull-opening member into a strip-shape which has at its one end a pulling tab and has a guide edge directed towards the opening edge of the ring-shaped member, and in addition extends to turn along at least half a circle of the opening edge.
Additionally, such an improvement wherein the pull-opening member is provided near the pulling tab with a notch or the like so as to create a weakened part for improving the initial opening property, and such an improvement wherein the pull-opening member is formed into a swirl shape for improving the tear opening property along a predetermined shape have been proposed by Japanese Kokai Utility Model Application Publications Sho No. 58-185526 and Sho No. 59-32666.
One of these proposed containers is shown in FIGS. 8 and 9. Namely, a closure shown in FIGS. 8 and 9 is made of a composite sheet comprising a metallic foil sheet such as an aluminum foil laminated with thermoplastic synthetic resin.
The closure covers an opening portion of a container barrel c and is fixed air-tight, by seaming or by fusion adhesion, to an opening end portion of the container barrel c through a ring shaped member b made of metal or plastic. A pull-opening member f in a strip-shape is made of a thermoplastic resin or the like, and is formed into an annular shape having at its one end a pulling tab e. The opening member f is more firmly fixed, by fusion adhesion or through an adhesive agent, to a region at the top surface of the closure that is defined within an opening edge d of the ring-shaped member b, than the tearing strength of the closure a.
If, in order to open the closure a, the pulling tab e is held and pulled upwards by fingers in relation to the closure a, an initial tearing for opening is brought about at a starting end g of a fixing portion between the pull-opening member f and the closure a.
If, after this initial tearing, the pull tab e is further lifted, a tear extending along an outside guide edge h provided on the pull-opening member f reaches the opening edge d of the ring-shaped member b, and a tear extending along an inside edge i of the pull-opening member f from a point x which is a starting point is produced in the closure a.
If the pulling tab e is further lifted, the tear which has reached the opening edge d is advanced along the opening edge d, and the tear which has extended along the inside edge i is advanced to nearly half a circle. As a result thereof, the closure a is loosened or slackened at the center region thereof, so that the advancing of the tearing along the inside edge i cannot be continued. Accordingly, the subsequent tearing stress is concentrated only on the portion extending along the opening edge d. As a result, the tearing advancing along the opening edge d is continued to the end, so that a complete tear-opening of the closure can be performed.
In addition, it frequently happens that this kind of container is usually kept for a long time in a comparatively high temperature environment in the summer. Even after the container is kept for a long time in such a high temperature environment, the removal of the pull-opening member from the metallic foil sheet must be avoided. In this respect, it is necessary that the initial strong adhesive strength therebetween be maintained for a long period of time in such a high temperature condition as mentioned above.
As for an adhesive agent which can be used for adhering to a metallic material such as a metallic foil sheet or the like, various investigations and searches have been heretofore made, and there has been proposed polyolefins, olefin copolymers, derivatives thereof and those containing a cross-linking agent. However, the former is so low in adhesive strength in relation to the metallic material that it is not suitable for practical use.
The latter requires a cross-linking treatment after being applied to the metallic material, so that the same cannot be suitably used for the container of the present invention.
On the other hand, it is known that an adhesive agent using a copolymer of an olefin--.alpha.,.beta. unsaturated carboxylic acid or ionomer resin, having carboxyl groups on its side chain can be firmly adhered by fusion adhesion to a metallic material. This adhesive has excellent moldability, and is tough and has good elasticity, and is also excellent in its wear resisting property and low temperature property. It also meets the U.S. FDA Standard and the Japanese Public Welfare Notification No. 20 (Feb. 16, 1982) so that it is suitable for use as an adhesive agent for a container for packing foodstuff.
However, according to the inventors' study, it has been found that a container with such an easy open type closure such that a pull-opening member f is adhered to a metallic foil sheet, as shown in FIGS. 8 and 9, by an adhesive agent using such a synthetic resin material as described above is so defective that after the container is kept in a high temperature environment such as the summer, if the pull-opening member f thereof is pulled upwards so that the metallic foil sheet may be broken open along the opening edge d of the ring-shaped member b, the tear advancing along the inside edge i goes underneath the pull-opening member f, before reaching as far as half a circle, so that the loosening of the closure becomes insufficient and consequently the tearing stress advancing along the opening edge d is dispersed, and as a result the tearing of the closure member a is made at an immediate region between the opening edge d and the pull-opening member f, and a piece of the closure member a remains unremoved at such a portion near the opening edge d that is near about 180 turning degrees from the initial tear opening portion as shown by imaginary lines in FIG. 8.
Additionally, it has been found that, if the container is kept for a long period of time, it frequently happens that the pull-opening member f pulls off from the closure member a in the beginning of the tearing operation.
As a result of the inventors' investigations about the cause thereof, it has been found that the main cause of the decrease in adhesive strength resulted from degradation, with a lapse of time, of the adhesive agent disposed between the closure a and the pull-opening member f. In addition, it has been ascertained that the decrease in the adhesive strength thereof with the lapse of time is fundamentally based on the fact that, while keeping and storing the container, the oxygen in the atmosphere invades and diffuses into the adhesive agent, so that the main chain of the copolymer resin is oxidized and becomes degraded.
Thus, in order to strongly adhere the metallic foil sheet and the pull-opening member f together, it is necessary to heat and melt the adhesive agent for a few seconds, several tens of seconds at a high temperature of about 160.degree.-230.degree. C., which is much higher than the melting point (70.degree.-120.degree. C.) of the adhesive agent. As a result, oxidation of the adhesive agent progresses beyond an induction period thereof, or in other words the time period of induction period to the point where degradation by oxidation takes place, that is, the period of time for keeping the container without degradation, after the foregoing fusion adhesion, is greatly shortened. Accordingly, even though the adhesive agent has a large adhesive strength immediately after the fusion of the adhesion, when kept at room temperature, the degradation thereof gradually progresses, resulting in a lowering in the adhesive strength thereof. This lowering in adhesive strength is especially remarkable at above 50.degree. C., and if the adhesive agent is used for adhering the pull-opening member f to the closure member a, there arises the problem of loss of use after a lapse of time of only about 2-3 weeks. This is based on the fact that the strip-shaped pull-opening member f is formed in a comparatively narrow strip shape, and therefore oxygen invades and diffuses into the adhesive agent layer from both sides thereof. The degradation is produced at the region of the adhesive agent layer which is located underneath and along the strip-shaped pull-opening member f.
Also, when considering the affinity between the pull-opening member f and the adhesive layer, it is preferable that the pull-opening member f and the adhesive layer are made of the same resins of the same quality. In this case, however, as a result of the foregoing degradation, with the lapse of time of this resin, there is the fear that the pull-opening member f itself will fracture or break off at the time of the tearing of the metallic foil sheet. Accordingly, in such a case where the pull-opening member f is made of a synthetic resin which is equal in quality to that of the adhesive layer, any measure for preventing the degradation, with a lapse of time, of the pull-opening member is necessary.
An object of the present invention is to provide a container with an easy open type closure wherein the foregoing inconveniences are eliminated, and an opening operation by tearing a metallic foil sheet made closure by means of a pull-opening member is carried out easily and reliably, and the entire area of the closure can be opened easily and reliably and definitely by causing the tearing to advance along an opening edge of a ring-shaped member in succession after an initial tearing.
Another object of the present invention is to provide a container with an easy open type closure, wherein a pull-opening member, adhered to a metallic foil sheet made closure for serving as container opening means is such that, even after the container is kept for a long period in a high temperature environment, when the pull-opening member is pulled upwards for opening the closure, there does not remain any piece of the closure portion along an opening edge of a ring-shaped member.
Another object of the present invention is to provide a container with an easy open type closure, wherein a pull-opening member is firmly fixed, through an adhesive agent layer, to a metallic foil sheet made closure, and even if the container is kept for a long time in a high temperature environment, the adhesive agent layer is not reduced in it adhesive ability.
Another object of the present invention is to provide a container with an easy open type closure, wherein a pull-opening member is made of a resin material which is not reduced in its tensile strength, even after the container is kept for a long time in a high temperature environment. Also, the pull-opening member is firmly fixed to a metallic foil sheet made closure through an adhesive agent layer which is not reduced in its adhesive strength with a lapse of time.
According to another aspect of the present invention, a specific adhesive layer is provided for a container with an easy open type closure of such an arrangement that a metallic foil sheet made closure is fixed provided together with a ring-shaped member on an opening end portion of a container barrel. Also a strip-shaped pull-opening member which has at its one end a pulling tab, and has an outside guide edge thereof directed towards an opening edge of the foregoing ring-shaped member, extends as long as at least one-half a circle of the opening edge of the ring-shaped member. The strip-shaped member is more firmly fixed to the top surface of the closure through the adhesive layer than the tearing strength of the closure. Advantageously, the adhesive agent layer is made of a resinous compound which is a copolymer of an olefin with an .alpha.,.beta. unsaturated carboxylic acid or ionomer resin which contains 0.01-0.5% by weight of a phenol series antioxidant.
According to another aspect of the present invention, a container with an easy open type closure is provided wherein a metallic foil sheet made closure is fixedly provided, together with a ring-shaped member, on an opening end portion of a container barrel. A strip-shaped pull-opening member has at its one end a pulling tab, and has an outside guide edge thereof directed towards an opening edge of the foregoing ring-shaped member, and extends at least one-half of a circle around the opening edge of the ring-shaped member. The strip-shaped pull opening member is fixed to the top surface of the closure utilizing an adhesive layer which provides a tearing strength which is greater than the tearing strength of the closure. The adhesive layer and the pull-opening member are respectively made of a copolymer resin of an olefin .alpha.,.beta. unsaturated carboxylic acid or ionomer resin, and the resin of the pull-opening member contains 0.01-0.5% by weight of a phenol series antioxidant and the pull-opening member and the adhesive layer are adhered together by fusion.